HP 6236A Operating And Service Manual page 23

Table 5-5. +20V Supply Troubleshooting
SYMPTOM
High output voltage
(higher than rating)
Low output voltage
(lower than rating)
STEP - ACTION
1. Attempt to turn down
loop by shorting 015 emitter-
to-base
2. Measure voltage at
OUt-
put of OR-gate (TP4).
1. Measure voltage at out-
put of OR-gate (TP4).
2. Measure voltage at TP8.
3. Measure voltage at TP7.
4. Measure voltage at TP13.
/
RESPONSE - PROBABLE CAUSE
a. If output voltage remains high, check 01, 015,
and CR9 for short.
b. If output voltage falls to near zero, remove short
from 015 and proceed to step (2).
a. If TP4 is approx. -0.7V, check for open CR6 or
R1, and defective U1.
b. :f TP4 is approx. +0.7V, check for defective 02.
a. If TP4 is between zero and -0. 7V, check for
open 01, 015, R14, or CR59, and defective 02.
b. If TP4 is approx. +0.7V, proceed to step (2).
a. If voltage at TP8 is positive, check Z1 for open
between pins 5 and 13, check R8 for open, and
check for defective R6 or U1.
b. If TP8 is approx. -0.7V, proceed to step (3).
a. If TP7 is approx. +0.7V, check CR6 for short.
b. If TP7 is approx. +1.4V, proceed to step (4).
a. If TP13 is approx. -0.7V, replace U1.
b. If TP13 is zero volts, check for open R10, and
shorted CR2 or CR3.
c. If TP13 is approx. +0.7V, check for open R2,
shorted R1, or leaky or shorted C2.
.
Table 6-6. -20V Supply Troubleshooting
SYMPTOM
STEP - ACTION
RESPONSE - PROBABLE CAUSE
NOTE: The +20V supply must operate properly
before troubleshooting the -20V supply.
High output vo1tage
1. Attempt to turn down
a. If output voltage remains high, check 03, CR29,
(more than 1 % greater
loop by shorting 013
and 013 for short.
than +20V supply)
emitter-to-base.
b. If output falls to near zero, remove short from 013 and
proceed to step (2).
2. Measure voltage at out-
put of OR-gate (TP5)
a. If voltage at TP5 is zero or negative, check for
defective 04.
b. If TP5 is positive, proceed to step (3)
5-9